Single patient use disposable carbon dioxide absorber which is patient tidal volume dependent and self-regulating

ABSTRACT

A single-patient-use disposable carbon dioxide absorbing and air treatment device is disclosed. Principal to the invention is an air impervious container having at least two openings for fluid communication between the inside and outside of the container. The container is also in fluid communication with a system for providing air to a patient by means of an airstream through a recirculating aided respiratory system. The container includes granular, carbon dioxide absorbing material, and may also include a bacteria filter. The airstream enters the container through the inlet opening and is dispersed into the granular material, where it is heated, humidified, and at least a portion of the carbon dioxide in the airstream is absorbed. The size and shape of the container and the amount of absorbent material are all preselected to provide for an immediate and optimal heating and humidifying effect and carbon dioxide removal. The airstream then exits from the outlet opening and is delivered to the patient without contacting regulator valves, pumps and the like, thereby avoiding heat loss and condensing of water vapor before the treated air reaches the patient. The construction is of sturdy, lightweight materials and the design is simple and straightforward, thereby minimizing the effort and training which would normally be associated with use of such a device.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 07/818,658 filed Oct. 28, 1991 now U.S. Pat. No. 5,360,002which in turn is a continuation-in-part of U.S. patent application Ser.No. 07/699,485 filed May 13, 1991 now U.S. Pat. No. 5,228,435.

BACKGROUND OF THE INVENTION

The present invention relates to carbon dioxide absorption devices usedin breathing assistance systems and more particularly to recirculatoryaided respiration systems for surgical or other medical applications,usually involving anesthesia.

In using recirculating breathing assistance systems, particularly withpatients who are experiencing breathing difficulty because of trauma,surgical procedures, anesthesia, or other reasons, it is generallydesirable to provide heated and humidified air to the patient. Warm,humidified air prevents "drying out" of the mucocilliary tissues of thepatient's respiratory system, and reduces patient heat loss that resultsfrom evaporation of water vapor from the lungs. It is also desirablethat the air provided to the patient be relatively free of anycontamination, especially contamination which may result from previoususe of the system by another patient.

Complicated, proven hazardous, and relatively expensive apparatus haveoften, been employed to condition the air supplied to a patient in arecirculatory aided respiration system. Where such a system is in usefor a surgery or other operating room procedure, anesthesia gases orother conditioning agents are often introduced into the stream of airinhaled by the patient. Also, any recirculation system requires theremoval of carbon dioxide from the air exhaled by the patient.

Such prior art systems for warming and humidifying air supplied to apatient often require the use of water reservoirs, heaters, andcomplicated delivery systems including complex electrical/electroniccontrols. Those systems may require complex hose connections andknowledge of the control systems; they may also require a significantamount of space in the operating room. Setup of these prior art systemscan be quite complicated, and the systems may require substantialcapital outlay as well as costly supplies. In such previousapplications, the use of heated humidifiers is prevalent in order toprovide proper conditioning for the air and entrained gases supplied tothe patient.

SUMMARY OF THE INVENTION

By proper utilization of the heat typically generated by the reaction ofcarbon dioxide with a granular absorbent material, such as soda lime,and by effective insulation, the typically expensive and oftentroublesome arrangements of a heated humidifier, water supply,reservoir, hose connection system, electronic monitoring and control,bulky mounting apparatus, and other generally complicated arrangementsas employed in the prior art can be much simplified or eliminated. Thecarbon dioxide removal, heating, and humidifying functions can also beisolated from an associated anesthesia machine in disposable fashion toprevent cross contamination between patients. The capability of asingle-use disposable device to warm, humidify and filter the air streamrecirculated to the patient, and to provide great flexibility andconvenience to medical personnel utilizing such a device is highlyadvantageous. One device providing some of these features and advantagesis the subject matter of a pending United States patent application,Ser. No. 590,967, filed on Oct. 1, 1990 by the inventor of the presentinvention. This invention is another device that achieves the samefundamental objects in a different manner with yet additionaladvantages.

The present invention relates to the heating and humidification of airto be supplied to a patient which eliminates electrical/electronichumidifiers, heaters, and other related apparatus, previously listed andgenerally required by previous procedures, to properly condition the airbefore it returns to the patient. In general, a device within the scopeof the present invention absorbs carbon dioxide from recirculated airmixed with anesthesia gases, and simultaneously warms and humidifies theair. The device can also include means for filtering out dust, virusand/or bacteria.

Nevertheless, the devices of the invention are simple and inexpensiveenough such that the complete carbon dioxide absorbing unit can bedisposed of after only a single patient use.

The single patient use device of the present invention does not requirethe flow control valves normally included in conventional carbon dioxideabsorption devices. Rather, any of the devices of the present inventionmay be utilized together with the elements of a conventionalrecirculatory aided respiration system having flow control valves, airbag, hoses, etc., to provide a carbon dioxide absorption capability forthe "life" of the soda lime or other CO₂ absorption material, afterwhich disposal of the single use unit of the present invention andreplacement by a new disposable unit ensues.

An important feature of the present invention is that the only portionof the aided respiration system which is discarded is that portion whichceases to be operational, i.e., the carbon dioxide absorbing materialitself and the container and hoses. Moreover, the device provides all ofthe features of a conventional aided respiration system having a carbondioxide absorber with the additional feature that replacement of thespent soda lime granules is performed quickly and easily with thedisconnection and reconnection of only two hoses.

The disposable device according of the present invention is thermallyself regulating; as more air is circulated, the air heating andhumidification increases. That is, the amount of heat generated in theexothermic reaction associated with CO₂ absorption correspondinglyincreases because of the increased quantity of carbon dioxide producedby the patient.

Specifically the self-regulating aspect of the present invention derivesfrom the fact that the source of heat and humidity is a directconsequence of the exothermic chemical reaction of carbon dioxide andthe soda lime. Carbon dioxide is derived from the metabolic reaction atthe biologic cell level and is delivered to the ventilating gas streamat the alveolar area of the patients lung. The amount of CO₂ produced isdependant on the patient's body weight and activity, which is minimalduring surgery. Consequently it can be seen that CO₂ is delivered in ametered dose as part of a tidal volume of gas passing from the patientto the respiratory system 10 and then on to the unit 40 at a ratecontrolled by the anesthesiologist. The reaction between CO₂ and sodalime produces 13,500 calories per gram molecular weight (mole) of CO₂(22.4 liters). Thus a known tidal volume of known CO₂ content combineswith a pre-selected amount of soda lime at a known reaction rate.Consequently the device can be considered to be self-regulating.

Insulation is preferably disposed around the device, the hoses, andother elements of the system to reduce heat loss. One such insulatingdevice for hoses is described and taught in U.S. patent application Ser.No. 07/019,248 filed Feb. 26, 1987 by the inventor Charles A. Smith andincorporated herein by reference.

Accordingly, the invention relates to a single-patient-use disposabledevice for removing carbon dioxide from, and increasing the moisturecontent and temperature of, air delivered to a patient connected in arecirculatory aided respiration system which system includes ananesthesia machine having an inlet flow control valve and an outlet flowcontrol valve. The system also includes an exhalation conduit throughwhich a stream of air exhaled by the patient flows to the inlet valve ofthe anesthesia machine, and an inhalation conduit through which a streamof air from the outlet valve of the anesthesia machines flows to beinhaled by the patient.

The device in its preferred form comprises a sealed, transparent, airimpervious container having an inlet opening and an outlet opening, anda mass of granular soda lime or other carbon dioxide absorbing materialwhereby air passing through the material to remove the carbon dioxidewill be warmed, humidified and filtered.

Specifically the invention includes in a recirculatory aided respirationsystem for patients, the improvement of a disposable single-patient useapparatus for conditioning air administered to a patient underanesthesia including an air impervious container located in immediateproximity to the patient having an inlet opening and an outlet opening,a mass of granular carbon dioxide absorption material disposed withinthe container in flow communication with the inlet opening and outletopening whereby air laden with carbon dioxide entering the containercontacts the carbon dioxide absorption material and whereupon carbondioxide is absorbed therein with the resultant generation of heat andwater vapor. The size of the container and the amount of carbon dioxideabsorption material is selected such that the normal breathing of apatient causes air to be freed of carbon dioxide and thus available tobe recirculated to the patient at a desirable humidification level andtemperature. The function of the container and material is selfregulating such that air at an acceptable temperature and humidity andcarbon dioxide level will be delivered compatible to the patient'sbreathing rate and tidal volume.

The amount of carbon dioxide absorbant material disposed within thecontainer could be as much as 3,000 grams. However, the preferred amountis in the range of 500 to 800 grams with 550 grams being the amount mostpreferred within the above range. Moreover, the air impervious containeris sized in the range of 1250 cc. to 1500 cc. of free air space.However, most preferred is a container size such that when it containsthe absorbant material it has a free air space in the range of between470 cc. and 1000 cc. The most preferred free air space in the containerwithin the above range is 750 cc.

Generally the container shape is preferred to be rectangular in planarcross section with the ratio of length to width being about 2 to 1.Moreover, the container shape in the vertical direction (ie. its depth)is determined most advantageously to terminate in a rounded bottom ordistal end, most conveniently the rounded bottom is semi-circular innature. The diameter of the circular portion is equal to the larger ofthe two planar dimensions, ie. the length of the container such that thecontainer has in essence a rounded bottom. Moreover, it has been foundto be advantageous that the depth of the container be greater than thelength of the container, generally a ratio of depth to width of 1.25 to1 being preferred. Moreover, advantageously the container can be sizedsuch that the ratio of planar cross section internal surface area to thedepth of the container is approximately 2 to 1 thus, providing optimalabsorbant utilization, space utilization, and optimal heat and watervapor output.

The air impervious container of the present invention also is preferablyconstructed of a rigid deformation resistant material. Many of the clearpolymeric resinous materials have been found to be suitable. Examplesinclude polystyrene, polypropolyene, ABS plastics, polycarbonates andthe like. The advantage of using such deformation resistant material isthat the sidewalls are restrained from bowing out and providingdimensional changes in the bed of absorbant material and also avoidingchanneling along the sidewalls of said container. In addition,channeling along the sidewalls of the container can be avoided byadhesively affixing a layer of carbon dioxide absorbant materialthereto. The result is that the sidewall is coated with the absorbentmaterial and the remainder of the bed interfaces with such coating toprovide air passageways similar to those present throughout the bed aswill be seen from the drawing.

The carbon dioxide absorbant material can be selected from any one ofthose commercially available. One such carbon dioxide absorptionmaterial is produced by Dewey and Almy Chemical Division of W. R. Grace& Co. and is sold under the tradename "SODASORB". Generally the materialincludes active ingredients of sodium hydroxide and hydrated lime.

The chemical neutralization of CO₂ with resultant production of heat andwater vapor is taught in the literature as follows:

(i) CO₂ +H₂ O══H₂ CO₃

(ii) 2H₂ CO₃ +2NA⁺ +2OH⁻ +2K+2OH⁻ ═2NA⁺ +CO₃.sup.═ +2K⁺ +CO₃.sup.═ +4H₂O

(iii) CA(OH)₂ +H₂ O══CA⁺⁺ +2OH⁻ +H₂ O

(iv) 2CA⁺⁺ +4OH⁻ +2NA⁺ +CO₃.sup.═ +2K⁺ +CO₃.sup.═ ══2CACO₃ +2NA⁺ +2OH⁻+2K⁺ +2OH⁻

In (i) the CO₂ dissolves at a rate governed by a number of physicalchemical factors. The rate is not proportional to the partial pressureof the CO₂ which is in contact with the film of moisture coating thesoda lime granules, but greater--because some of the CO₂ combineschemically with the water to form carbonic acid. The rate is directlyproportional to the rate of removal of dissolved CO₂, or H₂ CO₃, fromsolution, by reaction with hydroxyl ion (reaction ii). Thus the rapidityof removal of dissolved CO₂ is directly related to the availability ofhydroxyl ions. Since the reaction between H+ and OH- is instantaneous,forming water, reaction (iii) and (iv) must supply additional hydroxylions to keep the absorption of CO₂ progressing. The latter two reactionsare therefore rate limiting.

DESCRIPTION OF THE PRIOR ART

It has long been known that it is desirable to use a recirculatoryrespiratory system for anesthesizing patients. Such a system however,demands that carbon dioxide be removed from the patient's exhaled gasesbefore they are recycled. Moreover, ideally the gas should bereadministered to the patient in a warm humid condition to preventdrying of the mucus membranes and other post-operative complications.Several authors have identified this need as will be mentionedhereinafter.

One such author/inventor is Wayne W. Hay, inventor of the invention ofU.S. Pat. No. 3,088,810 issued May 7, 1963. The invention of the '810Patent is a conventional carbon dioxide absorber found in operatingrooms throughout the country. The apparatus is not directed towardhumidification and heating of the air although, admittedly the chemicalreaction disclosed above is taking place in the carbon dioxide absorberof the invention.

Another prior art reference is entitled "Humidification of AnestheticGases", by Chalon et. al. published by Carl C. Thomas, publisherBannerstone House, 301-327 East Lawrence Ave., Springfield Ill., U.S.A.1981, Library of Congress, Catalogue Card No. 8027492. Of particularinterest is FIG. 8.7 on page 76 and also FIGS. 10-2 and 11-3 showingprior art carbon dioxide removal and heating and humidification ofanesthetic gases.

Similarly are D'ery et. al. have addressed the subject matter of heatand moisture in air streams in an article entitled, "Humidity inAnesthesiology II. Evolution of Heat and Moisture in the Large CarbonDioxide Absorbers" at page 205 of The American Anesthesiology SocietyJournal Volume 14, No. 3, May 1967. Also Krister Nelson has addressedhumidification of the airways in a presentation at the Gibeck Meeting inStockholm, March 1991 as a member of the department of PediatricAnesthesia and Intensive Care, Ostra Sjukhuset, Gotenberg, Sweden.

Other references include an article entitled "Health Devices" publishedby ECRI, a non-profit agency, May 1983, Volume 12, No. 7 and U.S. Pat.No. 3,752,654.

Lastly, applicant is aware of "The Sodasorb Manual of Carbon DioxideAbsorption", published by W. R. Grace & Co., Dewey and Almy ChemicalDivision, copyright 1962.

The above references and the references disclosed in U.S. patentapplication Ser. No. 07/699,485 of which the present application is acontinuation-in-part and all of the references cited in any of theforegoing constitute all of the relevant prior art known to theinventor. It should be noted that none of this prior art teaches orsuggests the novel features of applicants invention which will behereinafter more fully described and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a recirculatory aided respirationsystem, constituting an anesthesia system, in which the presentinvention is incorporated;

FIG. 2 is an elevation view, on an enlarged scale, of a single-usedisposable carbon dioxide absorption device that comprises oneembodiment of the invention;

FIG. 3 is a detail sectional view taken approximately as indicated byline 3--3 in FIG. 2;

FIG. 4 is a detail sectional view taken approximately as indicated byline 4--4 in FIG. 2;

FIG. 5 is a sectional elevation view of the carbon dioxide absorberdevice of FIGS. 2-4;

FIG. 6 is a detail view, on an enlarged scale, partly in cross-section,of a portion of the device of FIGS. 2-5; and

FIG. 7 is an elevation view, similar to FIG. 2 of another embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The recirculatory aided respiration system 10 illustrated in FIG. 1,which is actually and anesthesia system, includes a conventionalanesthesia or "gas" machine 11. Machine 11 is utilized to provide adesired mix of anesthetic gases through a hose 12 to a fitting 13 thatis a part of the casing 14 of a device 15 that would normally servesystem 10 as a carbon dioxide "absorber", which is not needed whenemploying the present invention. Device 15 may be mounted uponanesthesia machine 11 by suitable means such as a bracket 16, as shownschematically in FIG. 1. There are two other tubular fittings 17 and 18at the top of the housing or canister 14 of device 15. A pressure reliefvalve 19 is connected by a hose 21 to fitting 17 and a manometer orother pressure indicator 22 is connected by a hose 23 to fitting 18.

The three fittings 13, 17, and 18 each communicate with an outletchamber 24 located, in the illustrated system, in the top of device 15.Device 15 has a undirectional outlet flow control valve 27 mounted inchamber 24 to permit only outward flow of air from chamber 24 through anoutlet port 26 into an inhalation hose or conduit 28, sometimes referredto as a rebreathing hose. A face mask 31 included in system 10 isconnected to conduit 28 so that a patient wearing the mask can receiveair, mixed with anesthetic gases, flowing to the patient in thedirection indicated by arrow 29.

System 10 includes another conduit or hose 32, sometimes referred to asan exhalation or exhaust conduit. Hose 32 extends from the patient'smask 31 to a T-fitting 33 that is connected to an inlet port 34 fordevice 15. Port 34 is in turn connected, by a unidirectional valve 38,to an inlet chamber 36 in the bottom of device 15. A rebreathing bag 37is also connected to the T-fitting 33. The flow of air through conduit32 and into the inlet chamber 36 of device 15 is in the directionindicated by arrow 39.

Device 15 includes a central chamber 41 separated from the outletchamber 24 by a wall 42 and separated from the inlet chamber 36 byanother transverse wall 43. Wall 42 is provided with a plurality ofapertures (not shown) to permit the flow of air from chamber 41 tochamber 24. Similarly, wall 43 includes a multiplicity of apertures (notshown) to allow the flow of air from inlet chamber 36 into centralchamber 41. In a conventional system the central chamber 41 would befilled with an absorption material; the CO₂ absorption materialtypically comprises granular soda lime, though some other proprietarycarbon dioxide absorption materials are occasionally used. In system 10,however, the chamber 41 of device 15 is empty.

As thus far described, system 10 would be quite conventional if thecanister, device 15, were filled with soda lime or some other CO₂absorber material. When the patient wearing mask 31 exhales, the exhaledair passes through conduit 32 to the inlet port 34 that leads into theinlet chamber 36 of the carbon dioxide absorption device 15 throughinlet flow control, check valve 38. A part of the air exhaled by thepatient may pass into the rebreathing bag 37.

When the patient wearing mask 31 inhales, air is drawn from the outletchamber 24 of device 15 through the outlet flow control valve 27 andoutlet port 26 into the inhalation hose or conduit 28. Additional air oroxygen anesthetic gases may be introduced into chamber 24 from machine11 to pass to the patient. The pressure in the system is held to anacceptable level by relief valve 19. Other controls may be provided,usually in the anesthesia machine 11.

A major problem with the recirculatory aided respiration systems, suchas the anesthesia system 10, is that the amount of carbon dioxideabsorption material that they utilize is very large and acts as a heatsink and a water vapor trap. For example, device 15 would present such aproblem if its chamber 41 were filled with soda lime. Moreover, theabsence of filter means leads to the entrainment of dust and even largergranules of soda lime or other carbon dioxide absorption material intothe air stream. This action is decidedly undesirable, particularly withrespect to possible effects upon the respiratory tract of the patientwearing mask 31.

Another problem of major proportions is that device 15, in theconventional system, should be replaced for each new patient to avoidinter-patient spread of contamination. Device 15 may be treated as asingle use device of this purpose, but it is really too expensive andcomplex for such use. Consequently, hospital and other service personnelare inclined to sterilize and recharge the device 15 with carbon dioxideabsorption material and use it repeatedly. This is a poor practice.Sterilization is difficult and adds to the expense of system operation.It may also be ineffective, to the decided detriment of the nextpatient. And the service personnel may simply neglect to sterilize oreven re-charge device 15, with potentially disastrous results.

Moreover, if such units are left standing for prolonged periods of timeafter an initial use unacceptably high levels of carbon monoxide aregenerated within the soda lime units which have a very deleteriouseffect on subsequent patients. In addition the absorption bed is soremote from the patient that any heat produced by the reaction betweencarbon dioxide and the absorbant material is completely dissipated intothe downstream hoses, valves and equipment. Similarly, humiditytransmitted to the air flowing through the absorption material is lostto downstream hoses, valves and equipment or condenses in conduit 28before reaching the patient.

To minimize and eliminate these problems the recirculatory breathingassistance system is properly sized and located in the immediateproximity of the patient to take full advantage of the CO₂ absorptionprocess. The present invention includes a simple inexpensive,single-patient-use, disposable device 40 for removing carbon dioxide,heating, filtering and humidifying the air delivered to the patientwearing mask 31. This device 40 is shown interposed in series in theinhalation conduit 28.

The CO₂ absorption device 40 includes container 48 having an air inlet44 and an air outlet 45, through which the air enters and exits whilepassing through the recirculation circuit. Container 48 is preferablymade from two pieces of transparent rigid deformation resistant materialwhich are sealed together, the seal providing openings 44 and 45 forcommunication between the outside and inside of the container.

Container 48 further includes a flexible holder 56 for supporting it inan upright position from a hook or other means (not shown). Suspensionof the container 48 is desirable so that it does not weigh down theconduit 28. Avoidance of weighing down of the conduit is desirablebecause any weight on conduit 28 pulls at mask 31 and causes discomfortto the patient or may cause container 48 to become disconnected fromconduit 28. Referring now to FIGS. 2, 3, and 4, the container 48 isshown in greater detail. Flexible holder 56 can be formed as aconsequence of the formation of container 48 by providing excessmaterial in the two sheets adhesively secured together or by a singleprojection or strap attached later. The flexible holder 56 can bedisposed between the arms formed by air inlet 44 and air outlet 45, orcan be attached at other suitable locations on container 48.

FIG. 4 shows in cross section an insulating layer 58 disposed on theinside of container 48.

Insulating layer 58 is preferably disposed on the inside of container48, but could be located on the outside thereof. Very typicallyinsulating layer 58 is made up of a closed cell foamed polymericresinous material examples of which are foamed polyethylene,polypropolyene, ABS, or polystyrene. Although any suitable insulatingmaterial could be used. Preferably it may be desirable to adhesivelysecure insulating material 58 to the interior side of container 48 underconditions where the insulating layer is positioned continuous aroundthe inner diameter of container 48 to block any potential air pathbetween the insulating layer and the container wall which may form orexist during construction or use of the disposable device or unit 40.Insulating layer 58 may also include a layer of reflective foil, betweenthe insulating layer and the container wall (not shown) which would tendto minimize radiant heat loss from unit 40 hereby serving toadditionally maintain heat within unit 40.

Insulating material 58 advantageously includes a viewing aperture orslot 50 for observing the color change in the CO₂ absorbant as it isconsumed. The slot may have champhored internal edges to avoid formingan air flow path when unit 40 is filled with CO₂ absorbing material. Ina preferred embodiment shown in FIG. 7, insulating layer 58 terminatesat a point above the bottom most part of container 40, but includes oneor more tabs 59 which extend from opposite sides of container 48 andproject downwardly along the side walls thereof in a buttingrelationship at the center line of container 48 to form stabilizing andlocating means 61 which prevent insulating layer 58 from slidingdownwardly in container 48 when insulating layer 58 is not adhesivelysecured to the sidewalls of container 48.

It is important that insulating layer 58 not be permitted to extenddownwardly to the full depth of container 48 since insulating layer 58by virtue of its presence may foster an air path either on its outsidesurface or its inside surface. The consequence of the formation of suchan air path generally leads to less effective air treatment anddetrimental downstream effects on the patient.

To further avoid the formation of such an air path granular carbondioxide absorbant material can be affixed to the inside surface of theinsulation layer 58 as shown in FIG. 7 at 63. Several commerciallyavailable non-toxic adhesive materials are available which are suitablefor such purpose. One such adhesive is manufactured by Ross ChemicalCorp. and sold under the tradename Wellbond. It should be understoodthat although it is desirable to affix the absorbant material on theentire inside surface of the insulating layer 58, only portions may beso treated.

Air inlet 44 includes a female joining member 60 attached to the airinlet 44 by a corrugated hose section 62, which may be a conventional 22mm. hose. Similarly, air outlet 45 includes a male joining member 64,attached to the air outlet 45 by a section of corrugated hose 66, whichmay also be a conventional 22 mm. hose. Corrugated hoses 62, 66 provideflexibility to the connection of the joining members 60, 64 to theconduit 28 or 32. Such hoses typically have a volume of approximatelyfifteen to seventeen cc per linear inch. Thus if a patient has a titlevolume of 750 cc's, it is desirable to have container 40 located inclose proximity to the patient such that, conduit 28 is no longer than88" and most preferably, that conduit 28 is no longer than 44". Thisarrangement ensures that warm humidified air will reach the patient uponthe second and subsequent breaths, the precise number of breaths beingcontrolled by the relative volumes involved.

As will be shown below, it is important that the air inlet 44 and airoutlet 45 be differentiated. Accordingly, disposing a female joiningmember 60 at air inlet 44 and a male joining member 64 at air outlet 45ensures only proper connection will be made of the device 40 into theconduit 28 of system 10. For example, to connect a device 40 into asystem 10, a conduit hose 28 includes a connection (not shown) withinits length of a male member within a female member, shown in FIG. 1 as70 and 72, respectively. The connection of members 70, 72 provides acontinuous passageway for an airstream through conduit 28. Thatconnection is first broken, and the male member 70 is inserted intofemale joining member 60 and the female member 72 is disposed over malejoining member 64, thus once again completing the air flow circuitthrough conduit 28. A connection of the separate sections of conduit 28to each other may thus be temporarily broken for insertion of device 40without creating stress to the breathing cycle of the patient.

Male and female joining members 64, 60 are thus associated with eachsection of conduit 28. Each of these can only be fitted onto the joiningmembers 72, 70 in one way, thus ensuring that the connection of thedevice is made properly. Such a system also provides flexibility in thatuse of the device 40 in system 10 may be omitted if air purification isnot desirable.

Moreover such a system permits very rapid error free disconnection of aspent unit and replacement with a fresh unit during an operation. It isnot required that a female joining member 60 be associated with the airinlet 44 and a male joining member 64 be associated with the air outlet45. The opposite relationship may be used even though such anarrangement may be contrary to conventional practice; the only importantconsideration being the consistency of the connections to ensure correctoperation of the device 40, as will be explained below.

Referring now to FIGS. 4 and 5, detail sectional views of the device 40are shown, partially illustrating the passively operating parts of thedevice 40. Similar elements shown in greater detail or in fullconfiguration will be identified by identical numerals between therespective Figures. FIG. 4 is a detail sectional view taken along line4--4 of FIG. 3, and showing in cross section the wall 74 of container48, insulating layer 58, and air impervious hose means or corrugatedhoses 62, 66. Disposed between the corrugated hoses 62 and 66 aregranules 76 of an absorbant material which absorbs carbon dioxide fromthe airstream flowing through the device 40. The CO₂ absorbant materialmay be soda lime or the like as is described above.

Referring now to FIG. 5, a partial sectional elevational view of thecarbon dioxide absorber device 40 is illustrated, showing both ends ofeach of the corrugated hoses 62, 66. Female joining member 60 definesone end of corrugated hose 62 and provides an air inlet 44 into thedevice 40. Similarly, the male joining member 64 defines one end of thecorrugated hose 66 which provides for an air outlet 45 from the device40. An airstream outflow opening 80 defines the other end of corrugatedhose 66.

As shown in FIG. 5, corrugated hose 66 extends well into the spacebounded by the container 48, and the airstream outflow opening 80 isdisposed as far as possible from the airstream inflow opening 78. Arrows84 indicate the flow of air into and through the granular material 76.The construction of nonwoven fiber material 96 is set forth in greaterdetail in U.S. patent application Ser. No. 07/674,682, filed on Mar. 21,1991, having common inventorship with the present invention. Thedisclosure of that application is incorporated herein by reference.

Outflow opening means 80 has outflow apertures 92 which permit theoutflow of the airstream from the granular material 76 into the openingmeans 80 as indicated by arrows 94. A filter means 96 covers outflowopening means 80 and is held in place by means of rubber bands 98.

As the arrows 84 and 94 indicate, the airstream must flow into andbetween the granular material 76 and must flow from the container 48 andinto corrugated hose 66 through outflow apertures 92. As will beexplained below, container 48 is a hermetically sealed enclosure inwhich the inlet 44 and outlet 45 are sealed to the corrugated hoses 62and 66 as is the edge 100 of the container 48. The airstream path, asshown by arrows 84 and 94, requires that the air pass through as much aspossible of the granular material 76 in container 48. This expends asmuch as possible of the carbon dioxide absorbent capability of thegranular material 76 because most of the material 76 comes into contactwith the passing airstream.

As a preferred embodiment the present invention contemplates that hose66 may terminate in a bacteria filter 97 which is in flow communicationtherewith. Several bacteria filters can be utilized as is are common inthe art. One such filter, commercially available is identified as model5000, manufactured by ARTEC Inc.

There are several advantages to locating a bacteria filter 97 within thecontainer 48 surrounded by granular material 76. One of those advantagesis that the bacteria filter 97 is kept at the surrounding temperature ofthe granular material which may exceed 110°. Consequently, the bacteriafilter is positioned so the condensation of water in the filter iseliminated and its life thereby, prolonged. Moreover, the filter can beselected such that its size and mass do not constitute a significantheat sink and thereby, do not disadvantageously affect the temperatureand humidity of the treated gas passing therethrough. In manyapplications it is advisable to provide for a screen 99 across the endof the filter to prevent any fine particles of the granular materialfrom passing into the bacteria filter and causing it to become pluggedand thereby shortening its life. If the above filter and screen systemare used filter means 96 may be eliminated.

Granular material 76 is comprised of large granules of soda lime or thelike. Soda lime changes color after its CO₂ absorbant capacity has beenexpended. Thus viewing aperture or slot 50 in insulating layer 58provides a view of the granules 76 through a clear wall portion of thecontainer 48. If the color change is sufficient to indicate that thegranules no longer can absorb a sufficient amount of CO₂, then thecomplete container 48 may be removed from the system 10 by disconnectingmale and female adjoining members 60 and 64 and replacing the container48 with a new container containing fresh CO₂ absorbing material 76.

In the operation of the unit of the present invention, it can be seenthat there are several advantageous features which constitute animprovement over the prior art. Specifically, as described earlier itbecomes very simple to interpose the unit 40 in a conduit carrying airto the patient. Because the unit is sized in volume and soda limecontent it is observed that initial charges of CO₂ containing gas intothe unit cause immediate heat and moisture evolution. This heat quicklybrings the CO₂ absorbant material to temperature and thereafter, heatsthe through flowing airstream to a desirable level. In addition, watervapor evolving from the reaction within unit 40 as well as water vaporcoming from water added to the absorbant material during its manufactureand water of hydration all contribute to the through flowing gas streambeing humidified to approximately 95%. This is contrasted to the normalhumidification level between 50% and 60% for conventional apparatus ofstandard operating conditions. Thus drying of the mucus membranes issignificantly reduced since humidification begins instantly after theunit is interposed in conduit 28. As described earlier, if approximately650 grams of soda lime are used in unit 40 ample reserve for CO₂ removalis afforded since approximately 100 grams of absorbant material isrequired per hour for a normal operation with the average operationlasting for approximately two to three hours.

Referring again to FIG. 7, it should be noted that ideally, theabsorbant material 76 advantageously does not fill the entire container48, but rather divides the container into an upper portion and a lowerportion 91 and 93, respectively. The lower portion contains the carbondioxide absorbant material while the upper portion remains empty or mayadvantageously be filled with an air pervious flow dispensing materialor air distribution means 95. The concept of having a manifold or airdispersing area above the carbon dioxide absorbant material plays asignificant role inasmuch as the air entering conduit 62 is more evenlydispersed across the entire bed thereby, causing a more uniformpenetration and utilization of the material 76. This air distributionmeans 95 in the upper portion 91 is but one way by which air flow isevened through the bed.

Other means to distribute the air relates to the fact that flow volumeis greater near the peripheral wall of container 48 than through thecenter of bed 76. This is true even if a free air space is providedabove the entire surface of the granular bed. The result is uneven useof the granular bed material due to the "wall effect".

The "wall effect" stems from the fact that gas flows more evenly over asmooth wall surface than through the tortuous channels formed by thecarbon dioxide absorbant granules. Normally the container wallconstitutes a smooth surface, thus the interface between the smoothsurface of the wall and the rough granular bed offers less resistance toflow than the paths between the granules.

To even the flow volume through the bed, methods are some times employedsuch as ridges and baffles along the peripheral wall to retard or extendthe flow path, thus promoting volume flow through the central portion ofthe granular bed. While somewhat effective in providing more uniform gasvolume penetration over the bed surface, there still exists adifferential in flow between the center and edges of the granular bed.The maximum flow rate differential between center and edge flowincreases in the container with a short depth and large circumference.Proper sizing of container 48 suggests that to remedy the problem oneshould advantageously change the wall circumference and depth. Thischange can be expressed in terms of a depth to surface area ratio. Ineffect, deepening the container and decreasing the surface area resultsin more even penetration of the entire granular bed and betterutilization of the material while minimizing the effect of any sidewallchanneling.

In the case of course granular material such as the soda lime 76,intergranular space is quite large compared to the granule size so arelatively insignificant increase in flow resistance results when thecontainer surface is decreased and container 40 is made deeper. Thesurface area to depth ratio of approximately 2 to 1 has been determinedto be advantageous in the present invention, thereby providing optimumgranule utilization, best space utilization, and optimal heat and watervapor output. Most preferred is a surface area to depth ratio in therange of 2.3 to 1, although other ratios have been found to beeffective. In the alternative to the earlier suggestion of adhesivelysecured granules 76 to the inner surface of the insulation layer it ispossible to texture the inner surface of container 48 or insulatinglayer 58 as the case may be, thereby eliminating the smooth surfacepresent in prior art devices.

In summary then, utilization of the present invention by interposing itin a conduit 28 permits the elimination of carbon dioxide absorbantmaterial in central chamber 41. Thereafter all of the air passing to thepatient passes through container 40. Since the average tidal volume ofan adult patient is approximately 750 cc and normally the time sequencefor a complete inhalation and exhalation is in the ratio of one third ofthe time elapsed for inhalation and two thirds of the time elapsed forexhalation. Container 40 can be optimally sized to take advantage ofseveral simultaneously occurring events, for example, if container 40begins with approximately 750 cc. of intergranular volume and free airspace, upon the first inhalation this treated air is transmitted to thepatient. Residual air in the device 15 is immediately drawn into theabsorber bed whereupon the carbon dioxide contained therein causes theevolution of heat and humidity. This heat and humidity serves tosaturate and heat unit 40 and its contents such that upon the secondinhalation and those subsequent thereto, the humidity and temperature ofthe air passing to the patient begins to rise. Subsequent inhalations oftreated air continue to provide the patient with warmer humidified airas the unit 40 approaches equilibrium. The insulating material preventsheat loss to aid the process of heating and humidifying the air supplyto the patient. Moreover, because the unit itself is compact it does notin and of itself constitute a large heat sink. Also because the bacteriafilter 97 is located inside container 40, it is kept at the temperatureof the granular bed therein, for optimal efficiency by elimination ofcondensation.

It has also been found advantageous to locate temperature sensing meansat strategic points on the outside of container 14. Typically, liquidcrystal dye temperature display units can be used. The temperatureindicating means serve to detect the heat of reaction between the carbondioxide absorbent material and the carbon dioxide itself. Thus, it ispossible to determine the areas of chemical reaction in the container.These temperature sensing units also serve as a backup or alternativeindicator of spent carbon dioxide absorbing material. For example, ifsoda lime, a common carbon dioxide absorbent material, is spent, itturns violet in color. However, upon sitting at room temperature for aprolonged period of time, the violet color disappears and the soda limeturns white again. If that soda lime is reused, in a container havingthe temperature sensors and no temperature increase is noted, noabsorption reaction will be taking place and consequently, the operatorwill know to remove the spent soda lime and replace it.

It should be noted that if the patient's tidal volume is greater than750 cc., additional air will be drawn into unit 40 through conduit 28from the device 15 and since the outlet conduit 62 extends well withinunit 40 to the bottom portion thereof, any air drawn from conduit 28will most assuredly be treated before it is inhaled by the patient. Thusthe unit is termed self regulating since the greater the patient's tidalvolume the more heat and humidity that is provided and the more air thatis treated.

It should be further noted that every effort is made to avoid downstreamvalves and metal components which would serve as heat sinks. Moreover,advantageously the insulated hoses disclosed and claimed in PatentApplication U.S. Ser. No. 07/593,555 can be employed.

Having thus described the invention what is claimed is:
 1. A carbondioxide absorber having an inlet and an outlet conduit, said absorberhaving self-regulating means for providing patient tidal volumedependent heated and humidified air to a patient, said self-regulatingmeans comprising: a container having an inlet opening and an outletopening connected respectively to the inlet and outlet conduits, apredetermined amount of carbon dioxide absorbent material disposedbetween such inlet and outlet openings, the container having a totalvolume of free air space when said scrubber material is disposed thereinof in the range of between 470 to 1000 cc's, said outlet conduit beingadapted to be connected to a patient and said outlet conduit having atotal volume equal to about twice the volume of free air space of saidcontainer and wherein the volume of said container is approximatelyequal to the tidal volume of a patient.
 2. The absorber of claim 1,wherein the amount of free air space in said container is approximately750 cc's.
 3. The absorber of claim 1, wherein the amount of carbondioxide absorbent material is not not more than 3,000 grams.
 4. Theabsorber of claim 1, wherein the amount of carbon dioxide absorbentmaterial is in the range of 500 to 800 grams.
 5. The absorber of claim1, wherein the amount of carbon dioxide absorbent material is about 550grams.
 6. The absorber of claim 1, wherein the volume of said containeris in the range of between 1,000 and 1,500 cc's.
 7. The carbon dioxideabsorber of claim 1, wherein said container includes at least onetemperature sensor.
 8. The absorber of claim 1, wherein said airimpervious container includes flexible holding means for supporting saidcontainer in operating position as part of a re-circulatory aidedrespiration system.
 9. The absorber of claim 1, wherein said airimpervious container is constructed of a rigid deformation resistantmaterial thereby resisting flexing, and dimension change of saidcontainer.
 10. The absorber of claim 1, further comprising means forproviding optimal absorbent utilization, space utilization, and optimalheat and water vapor output, said means for optimizing comprising theratio of internal surface area to depth of said container beingapproximately two to one.
 11. A method of removing carbon dioxide,heating, and humidifying air to be supplied to a patient connected in ananesthesia circuit based upon patient tidal volume comprising the stepsof:providing an air impervious container having an inlet and an outletopening; disposing a pre-determined amount of carbon dioxide absorptionmaterial between the inlet and outlet openings within the container, thecontainer having a volume of free air space of 470 to 1,000 cc when saidpredetermined amount of carbon dioxide absorbent material is disposedtherein; positioning the container in close proximity to a patient;passing exhalant air from a patient into said container through an inletconduit connected to the inlet opening; the exhalant air contacting saidpreselected amount of carbon dioxide absorber material in saidcontainer, and having the carbon dioxide removed therefrom to providescrubbed air; returning said scrubbed air to a patient through an outletconduit connected to said outlet opening where the volume of said outletconduit is not more than approximately twice the volume of the free airspace of said container such that based upon the patient's tidal volumeheated, humidified, low carbon dioxide air is delivered to the patientin a self-regulating fashion.